Re: Black Powder Pistol ?
Just so you know regular gun cleaning solvents are worthless on black powder guns unless they are water based. The problem is the salts, generated by the firing of black powder, are anhydrous and draw moisture from the atmosphere to rust the metal in the gun. The gun should be cleaned immediately after shooting it (a day later may be too late!) with soap and water which dissolves the salts, then with regular gun solvent, and then every part of it wiped down with an oily rag. Oil all the pivots with gun oil too. Failure to do this results in what you have.
I have a pistol similar to yours that I shot several times but really tired of the cleaning regime. I cleaned it completely and put it in a display case on the wall. I had bought mine as a kit and had to put about 40 or more hours into it to get the finish right and was proud enough of the results to display it. Needless to say I am NOT a fan of shooting black powder guns.